Au rif er ous wastes from the aban doned ar senic and gold mine in Z³oty Stok (Sudetes Mts., SW Po land)
Jan WIERCHOWIEC and Andrzej WOJCIECHOWSKI
Wierchowiec J. and Wojciechowski A. (2009) — Au rif er ous wastes from the aban doned ar senic and gold mine in Z³oty Stok (Sudetes Mts., SW Po land). Geol. Quart., 53 (2): 233–240. Warszawa.
The his tor i cal ar senic and gold-ore op er a tion at the Z³oty Stok mine gen er ated around 1 500 000 tonnes of wastes. The gold-bear ing post-flo ta tion tail ing dumps, waste slag heaps, mined rock and ar senic roast ing spoils (cin ders) from min ing of metamorphogenic, hy dro - ther mal As-Au de pos its have been ex am ined to eval u ate their gold grade. The waste ma te rial is dom i nated by calc-sil i cate skarn, dolomitic mar bles, serpentinites and As-Au ore frag ments. Sul fides are mainly loellingite, ar seno py rite and pyrrothite with some py rite, chal co py rite, sphalerite and ga lena. In ox i dized ma te rial, sul fides are rare or ab sent. Over 1000 sam ples of post-flo ta tion waste muds and three bulk sam ples of mined rock spoils were an a lyzed. Only tail ings show high con cen tra tions of Au (0.8–20.1 ppm) and As (1.0–2.6 wt.%). An av er age con tents of other met als (in ppm) are: Cu — 177.5; Pb — 212.2; Zn — 127.5; Ag — 0.38; Pt — 0.006; Pd — 0.001. An a lyt i cal re sults in di cate that con cen tra tions of these el e ments are very low along pro files, with no ob vi ous re la tion ship be tween con tent and depth. Av er age gold con tent of 0.3 ppm in waste slags dis qual i fies this ma te rial as a source of gold. The re main ing re sources of gold in the flo ta tion tail ings and waste heaps are es ti mated at as high as 2370 kg. The main pol lut ant is As with con tents ex ceed ing 52 100 ppm in the mined rock spoils.
Jan Wierchowiec, Fac ulty of Ge ol ogy, Uni ver sity of War saw, Al. Zwirki i Wigury 93, PL-02-089 Warszawa, Po land, e-mail:
Jan.Wierchowiec@.uw.edu.pl; Andrzej Wojciechowski, Pol ish Geo log i cal In sti tute-Na tional Re search In sti tute, ul. Rakowiecka 4, PL-00-975 Warszawa, Po land, e-mail: Andrzej.Wojciechowski@ pgi.gov.pl (re ceived: May 06, 2008; ac cepted: Jan u ary 12, 2009).
Key words: Sudetes, Z³oty Stok, wastes, au rif er ous tail ings, gold grade, re sources of gold.
INTRODUCTION
The Z³oty Stok (Reichenstein) re gion has been one of the most im por tant pre cious metal pro duc ers in the Sudetes since the late Mid dle Ages. How ever, some au thors be lieve that the be gin ning of min ing ac tiv i ties can be dated back to the 7–8th cen tu ries (Morávek, 1992).
Dur ing the pe riod 1540–1550, the Z³oty Stok mines pro - duced large quan ti ties of gold and were con sid ered among the rich est in Cen tral Eu rope. Since the be gin ning of the 18th cen - tury, gold ex trac tion as so ci ated with by-pro duc tion of ar senic took place for two hun dred years. At this time, the Z³oty Stok mine was the world’s larg est pro ducer of this metal (Dziekoñski, 1972). Min ing was car ried out in four ex ca va tion fields: the West ern Field (Góra Haniak), the Bia³a Góra Field, the Góra Krzy¿owa Field and the Góra So³tysia Field.
Ac cord ing to Ba³dys (1954), be tween 1481 and 1944 about 3 800 000 t of ar senic ores and from 9–13 t of gold were ex - tracted in the re gion. Af ter the Sec ond World War, eco nomic
gold-bear ing ar senic ores had an av er age ar senic con tent of up to 6 wt.% and yielded 3.2–3.5 g/t of Au. The mine was closed in au tumn 1961, due to the poor qual ity of the ar senic ores (Dziekoñski, 1972).
In the 1990s, ex ten sive ex plo ra tion in the sur round ings of the K³odzko–Z³oty Stok Massif pro vided new in sights into our knowl edge of the eco nomic po ten tial and evo lu tion of the Z³oty Stok area. De spite the long-last ing op er a tion, this gold-bear ing dis trict still has po ten tial for dis cov ery of Au-rich ar senic and other ores (Kanasiewicz, 1992; Muszer, 1992; Mikulski, 1996;
Wojciechowski, 1998; Speczik and Mikulski, 2001). Fur ther - more, gold con tents dur ing the me di eval and more re cent min - ing op er a tions has been a sub ject of nu mer ous stud ies (Wojciechowski, 1990, 1993, 1994; Muszer and
£uszczkiewicz, 1997).
The pur pose of this study is to pro vide data on the gold grade and to tal metal con cen tra tions in wastes of the Z³oty Stok min ing dis trict and to es ti mate the eco nomic po ten tial of these technogenic de pos its. Data are com pared with back ground lev -
Augering was the main method used to col lect over 1000 sam ples from dif fer ent tail ings dumps. 124 au ger holes were man u ally drilled into the ground to depths of up to 15 m. A cochleary-drill ing set (4 inch in di am e ter) was em ployed to drill through dumps and rep re sen ta tive sam ples were col lected at reg u lar 1 m in ter vals. Sur face-to-bed rock tail ing cores were chem i cally an a lyzed to eval u ate Au and As con tents vari a tions through the dump. Dur ing the drill ing, the cores were col lected and stored in her met i cally sealed bags.
Once in the lab o ra tory, the dried pri mary sam ples from each in ter val were di vided in a Jones type — rif fle split ter to sub-sam ples of about 100 g ac cord ing to the pro ce dure de - scribed by Gerlach et al. (2002). The sam ples were then sieved with a 0.06 mm sieve and over size par ti cles were ground in a ball-bear ing pulverizer.
Additionaly, bulk sam ples of 1000 ±50 kg from slag (one sam ple) and mined rock spoil (three sam ples) were col lected.
Each of the sam ples was run through a jaw crusher to ob tain grains smaller than 1 mm. Then sam ples were split by con ning and quar ter ing to sam ples of 10 kg. Af ter des ic cat ing, sam ples were di vided in a Jones split ter to 1 kg sub-sam ples, sieved with the 0.06 mm sieve and over size par ti cles were ground in the ball-bear ing mill. Geo chem i cal sam ples were pre pared for In - duc tively Cou pled Plasma (ICP) anal y ses us ing a stan dard pro - ce dure (Van Loon and Bare foot, 1991; Jarvis and Jarvis, 1992).
The gold and PGM con tents were de ter mined by fire as say (FA/ICP), and As, Mo, Cu, Pb, Zn, Ag, Ni, Co, Mn, Fe, U, Th, Sr, Cd, Bi, V, Ca, P, La, Cr, Mg, Ba, Ti, B, Al, Na, K and W by Atomic Emis sion Spec tros copy (ICP-AES) af ter aqua regia ex - trac tion from 100 gram of sam ple in tef lon bombs in the ACME An a lyt i cal Lab o ra to ries Ltd. in Van cou ver. The data de rived by an a lyz ing the sam ples from the wastes were used to cal cu late the mean weighted Au and As con tents as well as the to tal er ror in grad ing and as say ing anal y ses.
GEOLOGICAL SETTING
All au rif er ous wastes stud ied (post-flo ta tion tail ings, slag, ar senic roast ing and mined rock spoil) from the ar senic and gold mine at Z³oty Stok were de pos ited on frac tured meta - mor phic rocks of the Z³oty Stok–Skrzynka Tec tonic Zone, which is the north ern most unit of the L¹dek–Œnie¿nik meta - mor phic struc ture (Sawicki, 1956; Don, 1964; Cwojdziñski, 1975). This dis lo ca tion zone, de fined by Cymerman (1996) as the Z³oty Stok–Trzebieszowice (ZST) re gional shear zone, has a NE–SW trend and was de vel oped at the time of the Variscan de for ma tion.
The rock com plex of this unit is char ac ter ized in the Z³oty Stok area by the phe nom ena of cataclasis and mylonitization of vary ing in ten si ties. The ba sic rock com plex of the ZST shear zone is com posed of mica schists, mica-quartz schists
Stok (Cwojdziñski, 1974, 1975).
The late-tec tonic K³odzko–Z³oty Stok Massif is an in tru - sion of mixed granitoids of syntectonic-con tam i na tion type or i - gin de vel oped along dis lo ca tion planes with NW–SE trend, dur ing late phases of the Variscan orog eny (Smulikowski, 1979). The intruding magma had a high tem per a ture, as shown by reomorphic melt ing of the Haniak gneiss es, by in ten sive microclinization, and by the ap pear ance of cor di er ite and for - ma tion of migmatites within bi o tite schist (Cwojdziñski, 1975), it was also re spon si ble for ore-form ing metasomatic pro cesses on the Z³oty Stok As-Au de posit (Kowalski, 1963, 1969;
Wierzcho³owski, 1976).
The roof of the K³odzko–Z³oty Stok Mas sif is cov ered by rel ics of sed i men tary cover, now rep re sented by hornfelses, am phi bo lites, skarnoids and gneiss es. Re cently, some of these were re cog nised as having met al lo gen ic po ten tial (Mikulski, 2000; Speczik and Mikulski, 2001).
ARSENIC AND GOLD-BEARING MINERALIZATION
Three types of min er al iza tion are gen er ally rec og nized in the Z³oty Stok area: 1) loellingite-rich skarns which en ve lope stocks and lenses of dolomitic mar bles; 2) elon gated wedges of di op side-tremolite ore with patches and nests of ore min er als;
3) dis sem i nated ore re lated mainly to dolomitic mar bles, with sig nif i cant serpentinization.
This serpentinization, ac com pa nied by the for ma tion of sev eral va ri et ies of calc-sil i cate skarn-type rocks, was the crit i - cal pro cess for for ma tion of rich ar se nide ores (Muszer, 1992;
Niczyporuk and Speczik, 1993). The main ores in clude Au-bear ing loellingite, ar seno py rite, pyrrothite and mag ne tite with some py rite, chal co py rite, sphalerite and ga lena. The min - er al ized struc tures are 1 to 3 m thick (al though some reach 10 m) and are 700 to 2000 m long. Min er al iza tion is par tic u larly rich (up to 40% by vol ume) in sam ples with in creased amounts of or ganic ma te rial (Speczik and Mikulski, 2001). It is dom i - nated by large (2–4 mm) loellingite crys tals, which form pina - coids and prisms.
Dis sem i nated low-grade ores were found oc ca sion ally in on mined coun try rocks, mainly in mica schists con tain ing zones of graph ite, gar net and As-Au min er al iza tion. Ar senic min er als are com mon also in aplites, pegmatites, and other spessartite-bear ing vein rocks, which oc cur through out the area.
Na tive Au is ex tremely rare, oc cur ring mostly in car rier min er als as sub-mi cro scopic par ti cles. The chem i cally de ter - mined Au con tent in rich ar senic ores var ies from 15 to 35 ppm, and from 3 to 13 ppm for poor ores (Kowalski, 1961;
Budzyñska, 1971). Back scat tered elec tron and X-ray map ping of loellingite crys tals sug gest that gold is nearly evenly dis trib - uted through out loellingite crys tals (Niczyporuk and Speczik, 1993). Gold forms min ute in clu sions (0.5–5 mm) in loellingite, ar seno py rite, pyr rhotite, mag ne tite, Ni-Co sulphoarsenides,
quartz, gar net and li mo nite (Muszer, 1992; Niczyporuk and Speczik 1993; Mikulski, 1996). The most com mon form for in - di vid ual Au in clu sions in ar senic ore are oval Au grains in quartz which in cludes healed cataclased grains of loellingite. It is sug gested that Au dis persed in loellingite was remobilized and con cen trated in mi cro scopic quartz veins dur ing the later metasomatic stages, or as a re sult of hy dro ther mal ac tiv ity within shear zones dur ing post-Variscan time (Speczik and Mikulski, 2001).
The polymetallic de posit of Z³oty Stok also con tains ra dio - ac tive min er als, chiefly autun ite (Przylibski, 2001). The first anal y ses to ex plain the weak ra dio ac tiv ity of the rocks mined at Z³oty Stok were car ried out in the 1950s by the R-1 en ter prise from Kowary. In 1960, they re sulted in the dis cov ery of a lo cal - ity in the Bia³a Góra Field (Fig. 2) with an av er age ura nium con tent of 0.03 wt.% and a max i mum con cen tra tion of 0.2 wt.% (G³owacki and Kopeæ, 1963). The stud ies of Muszer (1995) have proved that ra dio ac tive min er als oc cur in the area of the Z³oty Stok de posit be tween the moun tains of Haniak (West ern Field) and Bia³a Góra (Bia³a Góra Field). The oc cur - rence of ura nium ore min er al iza tion in the form of a sec ond ary min eral, autun ite, has been con firmed in this area, while a pri - mary ura nium min eral (uraninite — UO2) has been found in the ore on the Z³oty Stok de posit. Its weath er ing caused the con - cen tra tion of autun ite around Bia³a Góra.
CHARACTERIZATION OF THE WASTES:
A REVIEW AND NEW DATA
Min ing and smelt ing of Au-rich ar senic ores in the Z³oty Stok area have gen er ated 1 500 000 tonnes of wastes, in clud ing flo ta tion tail ings, mined rock spoil, waste slag and ar senic roast ing spoil (cin ders) de pos ited in ponds (flo ta tion tail ings) and heaps. Wastes from min ing and smelt ing, of var i ous ages, are spread over a hilly area south and north of the town of Z³oty Stok (Fig. 2).
FLOTATION TAILINGS
Tail ings pro duced by a pro cess ing fa cil ity re main in four em banked de po si tion sites in the val ley of the Truj¹ca Creek.
Near the mine, along side the Truj¹ca Creek, 500 000 tonnes of sandy-silt tail ings were dis posed in the re ten tion ponds (dumps) that have spread with time over site.
Gold-bear ing tail ing dumps oc cur in the Truj¹ca Val ley, which is an ex ten sion of the Z³oty Jar Val ley. These tail ings are the waste prod uct af ter flo ta tion of crushed and milled ar senic ore at the treat ment plant of the ar senic smelter at Z³oty Stok.
Flo ta tion en rich ment was car ried out be tween 1935–1962 (un - til the smelter was closed down).
Fig. 1. Lo ca tion of Z³oty Stok min ing area on the back ground of the re gional geo log i cal struc ture
In all re ten tion ponds, the tail ings are to a var i ous de gree mixed with other prod ucts of the wet en rich ment pro cess. Un - pub lished data of the Ar senic Treat ment Lab o ra tory (ATL) from the pe riod 1958–59 show that the main ore com po nents of the flo ta tion con cen trate were loellingite, ar seno py rite and scorodite, fol lowed by gangue of ser pen tine, ol iv ine and quartz.
The ar senic con tent in the con cen trate ranged from 32.15 to 38.85 wt.% (the av er age of 12 sam ples was 36.02 wt.%). Ar - senic con tents in the gen eral wastes (ana lysed daily) ranged from 0.31–2.50 wt.% (the av er age of 30 sam ples was 2.04 wt.%). The av er age gold con cen tra tion in the above con - cen trate was around 10 mg/kg (10 ppm).
Post-flo ta tion waste muds fill four re ten tion ponds (marked as A–D in Fig. 2), lo cated over a dis tance of 1.2 km along the Truj¹ca Creek. The top o graph i cally high est pond D con tains the old est waste. The av er age thick ness of ar senic and gold-bear ing waste muds is 0.8 m in pond A, 5.7 m in pond B, 7.9 m in pond C and 9.9 m in pond D. The width of ponds var - ies from 100 to 300 m (Wojciechowski, 1990, 1998). Af ter 1962, pond C was used also to re tain bar ite wastes and pond D
as a col lec tor of the waste wa ter from the then fac tory of paints and var nishes.
Pre lim i nary data in di cate that the gold con tents in the dump of pond A was — 0.35 ppm, B — 0.52 ppm, C — 1.12 ppm and in dump of pond D — 1.86 ppm; while ar senic ranged from 2.0–2.6 wt.% (Wojciechowski, 1990, 1994). This study in di - cated that the av er age gold con tent in the flo ta tion tail ings is higher, while ar senic is lower. Gold con tents in these wastes ranged from 0.8 to 20.1 ppm Au. Pond B av er ag ing (arith me tic mean xa) 0.818 ppm Au, stan dard de vi a tion s = 198.83…, n = 27 ; pond C — xa = 11.833 ppm Au, s = 450.28..., n = 61 ; pond D — xa = 20.120 ppm Au, s = 551.02…, n = 36. Arsenium con - tents ranged from 0.97–2.57 wt.% As. Pond B av er ag ing (xa) 0.97 wt.% As, s = 0.26…, n = 27; pond C — xa = 1.66 wt.% As, s = 0.83…, n = 61; pond D — xa = 2.57 wt.% As, s = 0.85…, n = 36 (see Ta ble 1 and Fig. 3).
Cross-sec tions of the tail ing dumps show that three bed as - sem blages could be dis tin guished, that dif fer in gold and ar senic con tent. The bot tom beds have 200–500 ppb Au and 1.5–2.0 wt.% As, the mid dle sec tion con tains 1.8 ppm Au and
Fig. 2. Lo cal ity map show ing lo ca tion of sam pled wastes in the dis used ar senic and gold mine in Z³oty Stok area Min ing fields: W — West ern (Góra Haniak), BG — Bia³a Góra, GK — Góra Krzy¿owa, GS — Góra So³tysia
1.5–2.0 wt.% As, and the top part has sim i lar Au and As con cen - tra tions to the bot tom part. Er ratic Au and As con cen tra tions in the mid dle sec tion (Fig. 4) are prob a bly re lated to the re lease of waste pulp with dif fer ing con cen tra tions of these el e ments.
Sta tis ti cal treat ment of the an a lyt i cal data (n = 124) re - vealed a high cor re la tion be tween Au and As (co ef fi cient of cor re la tion of a re gres sion anal y sis r2 = 0.9598) and Au-Cu (r2 = 0.7905). On the other hand, no ob vi ous re la tion ship be - tween metal con tent and sam pling depth was found.
The av er age metal con tent in the pulp is low: Cu — 178 ppm, Pb — 212 ppm, Zn — 128 ppm, Ag — 0.38 ppm, Pt
— 0.0006 ppm and Pd — 0.001 ppm).
MINED ROCK SPOIL
The main spoil heaps, with an es ti mated vol ume of 360 000 m3, are lo cated near the shaft Jan in the West ern Field and near the en trance of the Gertruda adit in Z³oty Jar (Fig. 2).
The waste rocks com prise crushed black and green serpentinites, calc-sil i cates and other lo cal rocks in clud ing mas sive loellingite-ar seno py rite-py rite and pyrrotite ore (Muszer, 1992; Muszer and £uszczkiewicz, 1997).
Ac cord ing to Muszer and £uszczkiewicz (op. cit.), the av - er age con cen tra tion of met als in the waste heap in the West ern Field is — 1.76 ppm Au, 0.4 ppm Ag and 16 wt.% As.
Sub se quent de tailed sam pling was car ried by Wojciechowski (1998). His re sults are pre sented in Ta ble 2.
High Au and As con tents in sam ple 2 of Wojciechowski (1998) re sult from the fact that about 70 wt.% of waste here con sist of min er al ized rocks from the ore zone, in clud ing mas - sive ore hosted by green serpentinites. Sam ples 1 and 3 con tain
only mi nor min er al ized rock chips and the con cen tra tion of gold is re duced to 0.2 ppm. Con cen tra tions of Cu, Pb, Zn, Ag, in the sam pled ma te rial are low (<45, 25, 70, 0.3 ppm, re spec - tively). Con tents of Pt and Pd are be low the de tec tion limit.
Apart from these three waste heaps, the Z³oty Stok area con tains also nu mer ous small min ing waste bodies (hav ing an es ti mated vol ume of 25 000 m3), which are clearly seen in the lo cal to pog ra phy. Some rock spoil af ter me di eval gold min ing does not have ex pres sion in the mor phol ogy.
WASTE SLAG HEAPS
Slag heaps oc cur mainly in the Z³oty Jar Val ley (Fig. 2).
These are wastes af ter gold smelt ing in the Mid dle Ages. Au rif - er ous ar senic ore was smelted in prim i tive fur naces called
“dymarki” (Dziekoñski, 1972). Then the gold-bear ing sul fide melt ob tained (“crude stone”) was three times roasted to sep a - rate ar senic and sul fur, and to com bine the re main ing part with lead. The re sult ing gold-lead al loy was oxi dised to litharge, which flew to wards the cop ula of the cupellation fur nace, leav - ing me tal lic gold on the fur nace’s base. Two types of waste slag were pro duced dur ing this pro cess: a) slag af ter smelt ing au rif - er ous ar senic ore and b) slag af ter ox i da tion of lead and gold al - loy to litharge. To tal ton nage of slag around Z³oty Stok is es ti - mated at 30 000 t.
The av er age gold con tent in smelt ing slag var ies de pend ing on dif fer ent sources. Muszer (1992) re ported val ues of 0.5,
<0.5 and 3.0 ppm (n = 3); Wojciechowski (1993) pro vided val - ues rang ing from 0.1 to 0.35 ppm (av er age 0.19 ±0.05 ppm, n = 9); while Muszer and £uszczkiewicz (1997) gave val ues of 2.9 and 0.53 ppm (n = 2).
A bulk sam ple from one of the slag heaps in Z³oty Jar Val - ley re turned av er age val ues of 0.29 ppm Au and 1159 ppm As.
The con tent of other met als in the heap is low: Cu — <15 ppm, Pb — <20 ppm, Zn — <25 ppm, Ag — <0.3 ppm, and very low: Pt, Pd — <0.001 ppm, ex cept for rel a tively high (206 ppm) W con tent (Wojciechowski, 1998).
These re sults con firm ear lier data, which in di cated low Au con cen tra tions in smelter slags from the Z³oty Stok Mine.
ARSENIC ROASTING SPOIL (CINDERS)
To ob tain ar senic ox ide and sub se quently me tal lic ar senic the ar senic ores were roasted at tem per a tures of 740–800°C.
Gold con tained in the pri mary ore was con cen trated in roast ing spoil. The first at tempts to ex tract gold from the roast ing spoil
Ponds1 Con cen tra tion
n = num ber of bore holes Au [ppb] As [wt.%]
Pond B, n = 27 818 ±75 0.97 ±0.10
Pond C, n = 61 11833 ±113 1.66 ±0.21
Pond D, n = 36 20120 ± 80 2.57 ±0.28
1 — in drill cores from pond A the gold and As con tents were not de ter mined T a b l e 1 The av er age gold and ar senic con tent in the re ten tion ponds (dumps)
Fig. 3. Gold and ar senic con tents in the post-flo ta tion waste muds;
re ten tion ponds (dumps) marked as B, C and D
Bulk sam ple num ber
Lo ca tion (see Fig. 1)
Metal con tent [ppm]
Au As
1 S part of the waste heap in the
West Field 0.232 3279
2 S part of the waste heap in the
West Field 3.804 52120
3 waste heap near the Gertruda adit 0.167 2298 T a b l e 2 Weighted av er age con cen tra tions of gold and ar senic in the mined
rock spoils de pos ited in the heaps (Wojciechowski, 1998)
by amal gam ation, car ried out in the first half of the 19th cen - tury, were un suc cess ful. The plattner method was used to ex - tract gold from 1850. This method, with mod i fi ca tions, was used un til the 1950s. Ac cord ing to ATL data, gold con tents in roast ing spoil un treated for this metal ranged 19.2 to 34.8 ppm Au, av er ag ing (arith me tic mean ) 27.6 ppm Au, stan dard de vi - a tion s = 3.68 (n = 36). Gold con tents in roast ing spoil pre vi - ously treated for gold ranged from 2.0–12.0 ppm, av er ag ing 3.9 ppm Au, stan dard de vi a tion s = 2.36 (n = 36). Max i mum gold con cen tra tion in “post-sul fide” wa ter (liq uid waste af ter
chlo ri na tion of roasts in the Plat ter method) was 0.46 mg/l.
Chem i cally, roast ing spoil is dom i nated by iron ox ides (~60 wt.%) and sil ica, along with an av er age of 1.0 wt.% As.
The sam ples were ana lysed for Au and As only.
Af ter clo sure of the smelter in 1962, sev eral tons of roast ing spoil pre vi ously treated for gold were cov ered by a range of other waste ma te ri als and are cur rently a part of youn ger build ing em - bank ments. The main ar senic roast ing spoil heap is lo cated in the Truj¹ca Val ley, near the post-flo ta tion tail ing dump C (Fig. 2).
This type of waste was not an a lyzed in this study.
Fig. 4. Sche matic cross-sec tion through the flo ta tion dump C show ing the lo ca tion of core sam ples stud ied and con cen tra tions of Au (A) and As (B) in the sec tion
The lo ca tion of the dump is shown in Fig ure 2
CONCLUSIONS
The higher gold con tent in the flo ta tion tail ings com pared with a pre vi ous estimate (Wojciechowski, 1998) in creases their gold con tent from 1200 to 1380 kg.
Re sults of the cur rent sam pling of mined rock spoil in di cate close cor re la tion be tween Au, As and the pres ence of ore and min er al ized rocks from the ore zone.
The sam pling also con firms er ratic gold and ar senic con - cen tra tion in the an a lyzed ma te rial. Nev er the less a gold con tent rang ing from 0.16 to 3.80 ppm Au, av er ag ing 1.4 ppm Au (n = 3), is some what higher than pre vi ously es ti mated at around 1.3 ppm (Muszer and £uszczkiewicz, 1997). This al lows in - crease of the re main ing re source of the min ing waste heaps to about 990 kg Au.
Chem i cal anal y ses of smelter slag in di cated low Au con - cen tra tions with con tents rang ing from 0.2 to 0.4 ppm.
As ex pected, the high est As con cen tra tion (52 100 ppm) was found in the mined rock spoils (waste heaps). Slag ma te rial and tail ings also had high con cen tra tions of As, in the range of 9 650–25 700 ppm.
A relatively high grav ity-re cov er able gold value dur ing grav ity en rich ment of the flo ta tion tail ings and mined rock spoil (Muszer and £uszczkiewicz, op. cit.) in di cates good grav - ity amenability and may en cour age fur ther at tempts at gold ex - trac tion. Ex trac tion of gold through this pro cess may be prof it - able un der the pre vail ing eco nomic con di tions.
Ac knowl edge ments. We are very grate ful to S. Speczik and an anon y mous re viewer for crit i cal re vi sion of the manu - script and for very valu able com ments.
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